Here's some thought I have, based solely on how my MES performs. YMMV
. Other units could be different.
I don't believe there is any way the temp could be perfect at all positions on all the shelves. There could be a 25+ degree difference from the lowest to the highest shelf. Hot air rises, bottom shelf is right over a water filled heatsink
Higher temps on the vent side of the chamber, the heater and vent are on the same side. There would be more convection heating on that side of the unit.
The cycling of the controller can be +/- 10, which is a swing of 20 depending how much of a food load there is in there. Mine is usually within +/- 5 or less, I think adding charcoal in the wood box adds some BTUs which helps the heater cycle less. I also added an extra 600w heater to help the temp recovery when really loaded and in colder weather.
I usually flip and rotate the meat during the cook. If loading all the shelves with something like ribs, I'll swap the top and bottom shelves and the two middle shelves half way through the cook, then rotate the food on the shelf. I think this helps everything cook evenly.
Using meat probes and rotating/flipping meat should counteract most temp inconsistencies